Using a side access unit is a method to increase test coverage of a circuit board by allowing access through connectors, using LED sensors to detect LEDs or actuating switches that are mounted on the circuit board. Typically, these items are right angled devices.

A side access unit enables access using spring probes or mating connectors to access the components/electrical circuits of the board. This access can allow test coverage of components that otherwise may not be accessible with typical board test methods.

The engagement of a side access unit to the device being tested can be accomplished in several ways:

• Manual engagement where an operator actuates a lever.
• A roller and ramp mechanism so the test fixture is actuated, and the side access automatically engages into the devices that are being accessed.
• Pneumatics to drive the side access unit into the DUT.
• An electric motor to drive the side access unit into the DUT.

Depending on the quantity of devices and the types being accessed the type of engagement drive should be carefully considered.

An important factor when using a side access unit is the alignment of the unit to the circuit board and devices being accessed. It is critical to be aligned correctly so damage does not occur during engagement. The items of the side access that are making contact to components or mating connectors should self-align and allow for variations in mounting tolerances of the components and connectors.

The components or connectors of the DUT that are being accessed need to be right angled. Some connectors don’t have a good lead-in edge or angled edges that are used in alignment of the mating connector. These connectors can be difficult or impossible to engage using a side access unit. Connectors that have small contacts/pins might not be able to be accessed due to the potential for the contacts/pins to get damaged. The spacing of the contacts within the connector needs to be considered and the proximity of these contacts to the shell or plastics of the connector. If the contacts are too small, it may not be possible to access these using a side access unit.

Integrating a side access unit into your test can have a large impact on test coverage for your board. It may also provide pass/fail information on the solder joints of devices. Typically, if you need to test through connectors to obtain better test coverage then a side access unit can accomplish this for you.